This study investigates how deficits in attention and impulse control are reflected in the social and cognitive play of a 4-year-old boy with attention-deficit hyperactivity disorder. In addition, an A-B-A-B reversal design was employed to evaluate the effectiveness of dextroamphetamine (2.5 mg, twice a day) for treatment of preschool attention-deficit hyperactivity disorder. The most dramatic effects of medication were observed on the level of sustained attention and the pattern of cognitive play. Sustained attention during play and in a structured group activity improved, and play became more sequentially organized and symbolic. Results are discussed with respect to the following: 1) attention-deficit hyperactivity disorder and preschool play; 2) the efficacy of psychostimulant medication; and 3) the adequacy of teacher ratings versus direct observation in measuring medication response.